比较封装在列表内部自定义对象中的两个列表

Question

我有以下代码：

public class Person { 
  private String id;
  private String name;
  private List<House> house
}
public class House { 
  private String id;
  private String name;
  private List<HouseTask> houseTasks;
}

现在，我有两个房屋列表oldHouse和newHouse，这两个列表都填充了相同的房屋元素，但是嵌套的列表房屋任务在newHouse中更新了一个额外的任务。

如何获得一个新的列表addedTasksForHouse，该列表包含通过Java8流添加的任务？

这一直在破坏我的大脑，我似乎无法让它工作。

Answer 1

我觉得FlatMap可以解决你的问题

ArrayList oldHouses=新ArrayList

ArrayList newHouses=新ArrayList

//所有的房子

ArrayList AddedTaskForHouses=新ArrayList

         addedTasksForHouses = newHouses.stream()
        .flatMap(House-> House.gethouseTasks().stream())
        .collect(Collectors.toList());

//每家每户

ArrayList AddedTaskForHouse=新ArrayList

    addedTasksForHouse = newHouses.get(indexOfHouse).gethouseTasks()
                      .stream()
                      .collect(Collectors.toList());

如果这对你有用请告诉我

Answer 2

下面的代码做你想要的。

class Scratch {
    public static class House {
        private String id;
        private String name;
        private List<HouseTask> houseTasks = new ArrayList<>();
        //this new method returns the list of tasks that otherHouse has, but this house has not
        public List<HouseTask> findNewTasks(House otherHouse) {
            return otherHouse.houseTasks.stream()
                    .filter(ht -> !houseTasks.contains(ht))
                    .collect(Collectors.toList());
        }
    }

    static class HouseTask {
        //houseTask now has a name. this name is also used to compare HouseTasks to another, see the equals method
        String name;
        public HouseTask(String name) {this.name = name;}
        @Override
        public boolean equals(Object o) {
            if (this == o) return true;
            if (o == null || getClass() != o.getClass()) return false;
            HouseTask houseTask = (HouseTask) o;
            return Objects.equals(name, houseTask.name);
        }
        public String toString() {
            return "HouseTask: "+name;
        }
    }

    public static void main(String[] args) {

        //now let's create some example data:
        House h1 = new House();
        h1.houseTasks.add(new HouseTask("task1"));
        House h2 = new House();
        h2.houseTasks.add(new HouseTask("task2"));
        House h2changed = new House();
        h2changed.houseTasks.add(new HouseTask("task2"));
        h2changed.houseTasks.add(new HouseTask("task3"));

        //here you have the 2 inputs from your question. the second House in newHouses has the new task "task3".
        List<House> oldHouses = List.of(h1, h2);
        List<House> newHouses = List.of(h1, h2changed);

        //we now iterate over the two lists, taking a look at each house.
        //the difference in each house's tasks is collected into one resulting list
        //note: this assumes that the individual houses are at the same position in both input lists!
        List<HouseTask> taskDiffList = IntStream.range(0, oldHouses.size())
                .mapToObj(i -> oldHouses.get(i).findNewTasks(newHouses.get(i)))
                .flatMap(List::stream)
                .collect(Collectors.toList());

        //this prints "[HouseTask: task3]" since it's the only difference.
        System.out.println(taskDiffList);

    }
}